The potentiostatic intermittent titration technique(PITT) method was used to determine lithium ion diffusion coefficients in graphitized carbon fiber anode material as function of potentials. The plot of lg D vs E shows that the value of lithium ion coefficients in graphitized carbon fiber anode material has three minima, the least value obtained is 1 9×10 -13 cm 2/s.
Two expressions are introduced to calculate the lithium ion diffusion coefficients in graphite anode as a function of potentials when potentiostatic intermittent titration technique(PITT) is used. The lithium ion diffusion coefficients in graphite derived from effective surface area, which is measured by electrochemical method, are more reliable than those derived simply from radius of graphite particles(calculated from equation (3) and equation (2) respectively). The curves of dQ/dE vs E demonstrate that there are three reversible phase transitions during intercalation or deintercalation of lithium ion in graphite. In the vicinity of the potentials where phase transitions take place, the lithium ion diffusion coefficients in graphite material have three minima in the potential range 10～ 600 mV.
